South Sudan's top rebel military commander Simon Gatwech Dual returned to Juba on Monday in a key step forward in a floundering peace process, calling for an end to war.

"We are one South Sudan," rebel chief of staff Dual shouted, waving a walking stick in the air as he marched off the plane after landing in the capital, followed by over one hundred rebel troops.

The return raises hopes it will pave the way for the much delayed return of rebel chief Riek Machar, who is hoped to forge a unity government to help end over two years of an intense civil war marked by atrocities.

READ: Despair as Machar keeps Juba waiting

Dual was welcomed by top government army commanders, surrounded by heavily armed troops from both the government and rebels.

Guns and hugs

Tensions were high, but officers from rival sides gave each other the traditional Sudanese embrace, tapping each others' shoulders in a loose hug.

"We are here to implement the peace agreement," Dual said, referring to a repeatedly broken August 2015 deal.

He flew back on a specially chartered plane from neighbouring Ethiopia, where the force has been sitting a week waiting to travel amid furious arguments between the government and rebel leaders over the number of troops and the weapons they could carry.

READ: Weaponry wrangle delays Machar's return to Juba

Machar is due to forge a unity government with his arch-rival, President Salva Kiir, returning to the post of vice-president he was sacked from months before the violence began.

Both sides remain deeply suspicious, and fighting continues with multiple militia forces unleashed who now pay no heed to either Kiir or Machar.

Dual was welcomed by the commander of the presidential guards, General Marial Chanuong.

Both men have been sanctioned by both the UN and United States for their role in the more than two-year war in which tens of thousands have been killed.

Rebel spokesman William Ezekiel said that 195 troops landed along with Dual, to provide security for Machar, who he said hoped to return on Tuesday.

Some of the rebel troops looked visibly nervous, but others were more cheerful and raised fists into the air as their leader shouted "Viva SPLA, viva SPLM!" — the acronym for the army and ruling party divided by the war.

They came with their weapons, although they did not carry them off the airplane, as they were offloaded from the luggage hold direct onto a military truck.

Key international backers of the peace process are infuriated at his repeatedly delayed return, with the United States saying both sides have stalled the return of Machar.

Rebels however insisted the return of the troops on Monday showed their commitment.

"The arrival of the chief of staff means that the first vice president designate (Machar) can now follow," Ezekiel told AFP.

"We are sorry for all the delays, but this is South Sudan and, well, the world's youngest country is still learning."

Tens of thousands of people have been killed and more than two million driven from their homes in the conflict, which has reignited ethnic divisions and been characterised by gross human rights abuses.

Machar is currently at a rebel base close to the border with Ethiopia.

Minister of Information Michael Makuei told AFP that Machar was welcome to return to Juba, but had not yet been given a set time.

"The government is ever optimistic," Makuei said. "We are waiting for Riek Machar to come in at anytime."

The troops boarded three army buses to take them to one of three rebel army camps inside the capital.

The troops, who brought with them AK-47 assault rifles, as well as 20 machine guns and 20 rocket-propelled grenades, join a 1,370-strong armed rebel force already in Juba as part of the peace deal.

Government forces say they have implemented their promise to pull all but 3,420 of their troops from the city.

All other soldiers have to remain at least 25 kilometres (15 miles) outside the capital.